The fabrication and integration of multiple-wavelength semiconductor laser arrays is an integral part of the development of wavelength-multiplexed communication systems. A characteristic of such systems is that the system bandwidth increases proportionally to the number of multiplexed wavelengths, each of which can carry independent signals.
One current technique for developing devices suitable for these systems involves the fabrication of discrete sources having different wavelengths by varying the composition of the active layer of each laser source. For example, by varying the indium concentration of InGaAsP active layers, the wavelength can be varied from 1.3 .mu.m to 1.55 .mu.m. This technique, however, is limited by the difficulty in closely spacing the wavelengths (channels), and by the difficulty in integrating such sources into an array.
Additionally, discrete or integrated multiple laser arrays can be fabricated using internal gratings to make distributed feedback (DFB) or distributed Bragg reflector (DBR) lasers. Two techniques can be used: a) varying the grating periodicity from laser to laser, which is difficult to achieve with holographically defined gratings; and b) making wavelength-tunable (multiple-section) lasers. Such an integrated array has been demonstrated by Koren et al. in "Wavelength division multiplexing light source with integrated quantum well tunable lasers and optical amplifiers, " Appl. Phys. Lett. 54, pp. 2056-2058 (1989).
A multiple-wavelength array based on surface-emitting, short-wavelength (about 1 .mu.m) lasers was recently reported by Chang-Hasnain et al. in "Surface Emitting Laser Arrays with Uniformly Separated Wavelengths," Conf. Digest of the 12th IEEE Intl. Semi. Laser Conf., Davos Switzerland, pp. 18-19 (1990). However, the wavelength of this array is inappropriate for most communication systems, and cannot be easily extended to the preferred wavelength range of 1.3 to 1.55 .mu.m. Moreover, the fabrication complexity of such an array limits its yield, reliability, and practicality.